It CAN be done but you will definitely NOT like the price and hassle of trying to get things right even if you do all the work yourself. Using stock parts.
The easiest way to go 4WD on your truck would go with an older solid Toyota solid front axle and leaf springs, then choose the transfer case from there, still a lot of fabrication, as after the front is done you will have to lift the rear to match it.
Your best bet would be to go with a truck already equipped with 4WD and do your desired swaps and upgrades from there.